The House Judiciary Committee subpoenaed former Trump administration aide Rob Porter on Monday to testify in its probe regarding possible obstruction of justice by President Trump.

Why it matters: Porter was a key witness for the obstruction portion of former special counsel Robert Mueller's investigation. He resigned from the White House last year after his 2 ex-wives came forward with abuse allegations. Porter may never have to face the committee as the White House has moved to block other former surrogates from testifying before the House Judiciary.

The number of House Democrats who have publicly expressed support for an impeachment inquiry has quietly crept up to 117 — an average of one a day for the month of July that brings the caucus one short of a majority, just in time for August recess.

Why it matters: The slow-drip of lawmakers joining the impeachment fray, boosted in waves by the Mueller hearings and President Trump's racist outbursts, disguises the reality that momentum has tilted squarely in favor of a formal inquiry.

Driving the news: Florida Rep. Ted Deutch wrote in the Sun Sentinel this morning that "the question is no longer whether the House should vote to proceed with a formal impeachment inquiry. The inquiry has already begun."

Deutch is referencing a recent court filing in which the House Judiciary Committee wrote that it had already begun "investigating whether to recommend articles of impeachment."

The big picture: Deutch, the chairman of the House Ethics Committee and a member of House Judiciary, is not the only influential Democrat to come out in favor of an impeachment inquiry this week.

Foreign Affairs Chair Eliot Engel (N.Y.), who heads one of six committees that Speaker Nancy Pelosi has tasked with investigating the Trump administration, bucked leadership in calling for an inquiry on Wednesday. Appropriations Chair Nita Lowey (N.Y.) joined him later that afternoon.

Between the lines: Many have viewed Pelosi's reluctance to launch impeachment proceedings as a means of protecting the swing-district Democrats who were key to winning back the House majority in November. But if those very lawmakers are taking it upon themselves to call for impeachment, Pelosi may soon find her stance obsolete.

What to watch: The fall is widely seen as Democrats' last chance to move forward with a formal inquiry before election season begins in earnest. As members return home, four national progressive groups tell BuzzFeed News they're launching a campaign to pressure wary Democrats on their impeachment stances through town halls and local events.

"Luján’s support for impeachment proceedings could help unlock the backing of a slew of freshman Democrats who Luján helped get elected in 2016, when he ran Democrats’ campaign arm ... And Lewis’ support would carry significant sway with members of the Congressional Black Caucus who have remained on the fence so far."